The present invention relates to a method for manufacturing a multilayer ceramic capacitor, and more particularly, to a method for manufacturing a multilayer ceramic capacitor by injecting electrodes into pore layers formed among the dielectric layers through sintering process. The pore layers are reduced and the surface energy of the pore layers is raised so that spontaneous injection or implantation of molten metal for forming the internal electrodes is possible without applying high pressure.
In general, multilayer ceramic capacitors are not only widely used compared to other types of capacitors due to the relatively high dielectric constant of titanic acid barium which forms the dielectric, but also due to the high static electrical capacity per unit volume.
Multilayer ceramic capacitors are made by alternately stacking a number of thin dielectric layers and internal electrodes. There are two general methods for manufacturing multilayer ceramic capacitors. In one method, the materials for the internal electrodes and ceramic dielectric are sintered simultaneously. In the second method, an electrode material is injected or implanted after sintering the dielectric material.
In the first method of simultaneously sintering the electrode and dielectric materials, an electrode-forming paste of precious metals, such as platinum or gold, is applied on one surface of the thin ceramic dielectric layers or sheets. A number of these sheets, rectangularly shaped, are stacked and subjected to sintering at a high temperature to manufacture the ceramic capacitor. This method uses expensive precious metals, such as Au, Pd, and Ag/Pd, which are stable in a high temperature oxidization atmospheric environment, as internal electrode materials. Not only is manufacturing cost high there are problems in low manufacturing yields since these electrode materials have different thermal expansion coefficients than the dielectric material, which cause contact problems between the internal electrodes and dielectric upon sintering.
In order to avoid the problems encountered in this simultaneous sintering method of electrode and dielectric, alternative methods for manufacturing a ceramic capacitor in which expensive precious metal electrode material is not used must be found. In place of the electrode material layers, open-structured or pore layers are formed among dielectric layers so that molten metal may be injected into the pore layers to form the internal electrodes. This method is described in U.S. Pat. Nos. 3,679,950; 3,965,552; 4,030,004; and 4,353,957.
According to this method of injecting molten metal into the pore layers, a quasi-electrode material, which includes organic substances, is applied by painting or screen printing on a large number of ceramic dielectric rectangular sheets. The sheets are stacked and a sintering process is performed to obtain the pore layers by the combustion of organic substance. Then molten metal, such as tin, copper, aluminum, lead, arsenic and indium, is injected into the pore layers to form the internal electrodes of the capacitor. The manufacturing cost of this method is less than the simultaneous sintering method with precious metal internal electrodes. In the pore layer process, relatively low-priced metals, such as tin and the like, are used for electrode material. There is a further advantage in that a dielectric which is fine in structure and high in dielectric index can be obtained by performing the sintering process at high temperatures.
However, according to this method, high pressures over 10 atmospheres must be applied for injecting the molten metal into the interior of the pore layers formed through sintering. Complex equipment must be installed and the manufacturing process is complicated by such high pressure requirements. Consequently, mass production of capacitors with this method is difficult.